1. Field of the Invention
The present invention relates to a clutch cover assembly having a support member which supports a conical spring in engagement with a diaphragm spring.
2. Description of the Related Art
In general, a clutch cover assembly is mounted on a flywheel of an engine and is used to transmit a drive force of an engine to a transmission. Such a clutch cover assembly is mainly composed of a clutch cover fixed to the flywheel, a pressure plate for clamping a frictional member of a clutch disc assembly against the flywheel, and a biasing member for biasing the pressure plate toward the flywheel.
In general, a diaphragm spring is used as the biasing member mentioned above. The diaphragm spring is composed of an annular spring portion and a plurality of lever portions extending radially inwardly from the inner circumferential edge of the annular spring portion. The diaphragm spring biases movement the pressure plate such that the pressure plate is urged into engagement with the flywheel. When the lever portions are pressed, the diaphragm spring is moved to release its biasing force from the pressure plate.
The force required to dis-engage the clutch is generally equal to the force imparted by the diaphragm spring on the pressure plate. Upon release of the biasing force from the pressure plate, the release load required to continue movement of the diaphragm spring increases as the displacement of the diaphragm spring continues in a relationship generally defined as force displacement characteristics of a spring. Each type of spring has its own force displacement characteristics. For diaphragm springs, at a certain critical point (the peak point), the release load decreases gradually, and again gradually increases at another certain critical point. In a clutch cover assembly, it is desirable for the peak point (the maximum load) of a diaphragm spring to be set such that the peak point corresponds to the clutch mechanism being between an initial clutch engagement position (where a clutch disc is new and has a maximum thickness) and a clutch engagement position where a frictional member of the clutch disc assembly is worn. Therefore, when the frictional member is worn, the release load required to disengage the clutch mechanism may increase as the clutch becomes worn.
Recently, a clutch cover assembly has been fitted with a conical spring improves the release load characteristics. Such a conical spring biases the diaphragm spring in a direction away from the pressure plate. In this case, the release load of the diaphragm spring and the release load of the conical spring are combined. Therefore, the combined release load can be optionally altered by selecting a conical spring having a appropriate load characteristics. For example, at the stroke position where the release load of the diaphragm spring is large, by combining the release load of the diaphragm spring with the release load of the conical spring to reduce the composite load, it is possible to obtain flat release load characteristics where the change of load is suppressed. In other words, when the frictional member is worn, the force required to step on the clutch pedal is hardly changed and the operational feeling upon the release operation is therefore enhanced.
In the conventional clutch cover assembly described above, wire rings are used to support the diaphragm spring from the pressure plate side and a separate a support member such as a support plate is used to support the conical spring. Therefore, the structure for improving the release load characteristics is complicated.